In communication networks, information in the form of data is typically passed between endpoints. In order to achieve this, the data is often routed using one or more switches. Conventional switches may be used to establish circuits across the network or to route data units, typically formed as packets. Known circuit switches include space division switches, time multiplexed switches, S-T-S (space-time-space) switches; and T-S-T (time-space-time) switches. Known packet switches include asynchronous transfer mode (ATM) switches; internet protocol (IP) routers; and the like.
Both circuits and packets may be switched using a switch having buffers cyclically interconnected to inputs and outputs by way of commutators. Such switches are referred to as rotator switches. Example rotator switches are described in U.S. Pat. No. 4,470,139, entitled Switching Network For Use In a Time Division Network and U.S. Pat. No. 5,168,492, entitled Rotating-Access ATM-STM Packet Switch, the contents of both of which are incorporated herein by reference.
Conventional rotator switches transfer data at a plurality of inputs to tandem buffers each having multiple storage locations. At any time, each input and each output is interconnected with a single buffer. The interconnections of inputs to buffers, and outputs to buffers are cycled synchronously so that each buffer is interconnected with each input and each output once in a rotator cycle. Each output is associated with a specific storage location in each buffer. The storage location for any one output is typically the same for all buffers. Data at an input may quickly be transferred to a destination output by transferring the data to the tandem buffer currently interconnected with the input in the storage location associated with the destination output, if this storage location is available. When this tandem buffer is next connected to the destined output, the output receives this data. Thus, a non-blocking n×m circuit switch may readily be formed with n buffers, each including m storage locations.
In a rotator switch that switches packets, the storage location associated with the destination output for any one packet may not be available. As such, rotator switches suited to switch packets may queue packets until a tandem buffer whose storage location associated with this destination is available is interconnected. Conveniently, rotator switches used to switch packets typically include more buffers than inputs and outputs. They also cycle inputs to buffers and outputs to buffers at a higher rate than the rate at which packets arrive. So, with a proper number of tandem buffers there is limited delay in switching the data. This is detailed in the above noted U.S. Pat. No. 5,168,492.
Many conventional switches also include redundant hardware. In this manner, if a fault occurs, redundant hardware may be used in place of the failed hardware. Typical rotator switches, however, do not include redundant elements. Though, rotator switches used to switch packets do typically include more buffers than inputs and outputs. For such switches, a failed buffer can simply not be used. This reduces the efficiency of the switch. Rotator switches used to switch circuits, however, typically include just enough buffers to route data from inputs to outputs. As such, absent other error or fault control mechanisms, once a fault occurs at an input, output or within a buffer of a rotator switch, there is little opportunity to recover from the fault without operator intervention.
Accordingly, there is a need for an improved rotator switch including one or more redundant elements that is capable of reacting to faults within the switch.